1. Field of the Invention
The present invention relates to a carbon fiber precursor fiber bundle comprising monofilaments of an acrylonitrile-based polymer that is applicable in manufacturing a carbon fiber bundle for use as reinforcing material in a fiber reinforced composite material.
This application is based on Japanese Patent Application No. 2000-190150 and Japanese Patent Application No. 2000-201535, the contents of which are incorporated herein by reference.
2. Description of Related Art
Carbon fiber, glass fiber, aramid fiber, and the like, are used in a fiber reinforced composite material. Among the aforementioned, carbon fiber is superior in relative strength, relative modulus of elasticity, thermal resistance, chemical resistance, and the like, and is used as reinforcing material in a fiber reinforced composite material for use in sporting equipment such as in golf shafts and fishing rods, as well as for general industrial purposes such as in aircraft, and the like. Such fiber reinforced composite material is manufactured, for example, according to the following method.
Initially, in the baking process (oxidizing process), a carbon fiber precursor fiber bundle comprising monofilaments of acrylonitrile-based polymers undergoes baking at 200 to 300xc2x0 C. in an oxidizing gas, such as air, to yield a flame-resistant fiber bundle. Subsequently, in the carbonizing process, the flame-resistant fiber bundle is carbonized at 300 to 2000xc2x0 C. under an inert atmosphere to yield a carbon fiber bundle. This carbon fiber bundle is processed, as necessary, into woven cloth, and the like, which is then impregnated by a synthetic resin and formed into a predetermined shape, to obtain a fiber reinforced composite material.
A precursor fiber bundle used in manufacturing a carbon fiber bundle is required to possess a high compactness such that, during the baking process, the monofilaments comprising a fiber bundle do not unravel and get entangled with neighboring fiber bundles, or alternatively stick to the roller. However, the resultant carbon fiber bundle obtained from a precursor fiber bundle having a high compactness possesses a problem in that it is very difficult to impregnate with resin due to its high compactness.
In addition, a carbon fiber fabric obtained by weaving carbon fiber bundles must be a fabric with as few apertures as possible, so as to avoid creating voids in the resin, at the time of impregnation by the resin. As a result, a tow spreading process is performed either during or after weaving. However, a carbon fiber bundle obtained from a precursor fiber bundle with high compactness possesses a problem in that tow spreading is extremely difficult due to its high compactness.
As a precursor fiber bundle that has a high compactness, and which can provide a carbon fiber bundle having a tow spreading ability, Japanese Patent Application, First Publication Laid Open No. 2000-144521 discloses an acrylonitrile-based fiber bundle comprising acrylonitrile-based polymers containing at least 95 wt. % of acrylonitrile, in which the total denier is at least 30,000, with 2 to 15 essentially continuous wrinkles, each of which is 0.5 to 1.0 xcexcm in height and extends in the longitudinal direction on the surface of the fiber bundle, wherein the absorption volume of iodine per fiber weight of the fiber bundle is 0.5 to 1.5 wt. %.
This precursor fiber bundle is obtained by means of extruding a spinning solution which is a solution of an organic solvent and an acrylonitrile-based polymer to a first coagulation bath formed from an aqueous solution of an organic solvent comprising an organic solvent concentration of 50 to 70 wt. % and a temperature of 30 to 50xc2x0 C. to form solid fibers. Solid fibers are then taken-up at a take-up speed no greater than 0.8 times a extrusion linear speed of the spinning solution from the first coagulation bath. Subsequently, solid fibers are placed in a second coagulation bath formed from an aqueous solution of an organic solvent comprising an organic solvent concentration of 50 to 70 wt. % and a temperature of 30 to 50xc2x0 C., and drawn by 1.1 to 3.0 fold, thereby yielding the precursor fiber bundle.
However, the compactness of this precursor fiber bundle and the tow spreading ability of the carbon fiber bundle obtained from this precursor fiber bundle are inadequate. In addition, the carbon fiber woven material requires a uniform texture with few apertures, and thus a carbon fiber bundle having a high bulkiness is required.
In this manner, a carbon fiber precursor fiber bundle having a high compactness and excellent carbonizing processing ability, which is able to provide a carbon fiber bundle possessing an excellent resin impregnating ability, an excellent tow spreading ability, a high strength and high bulkiness, is required.
In addition, with respect to the cloth of carbon fiber, since a favorable external appearance and handling is also in great demand, in addition to the above-mentioned functions, it is necessary to also provide xe2x80x9ccovering abilityxe2x80x9d to the carbon fiber. In order to simultaneously provide the aforementioned resin impregnating ability, tow spreading ability, and covering ability at the time of forming a cloth, it is necessary to impart a high bulkiness to the carbon fiber bundle. Hence, in order to further improve the resin impregnating ability, tow spreading ability, and covering ability, it is necessary to further improve the bulkiness of the carbon fiber bundle.
Accordingly, it is a first object of the present invention to provide a carbon fiber precursor fiber bundle having a high compactness and excellent carbonizing processing ability, which is able to provide a carbon fiber bundle possessing an excellent resin impregnating ability and tow spreading ability, in addition to a high strength and high bulkiness.
In addition, it is a second object of the present invention to provide a carbon fiber precursor fiber bundle which is able to provide a carbon fiber bundle possessing an improved bulkiness, in addition to a superior resin impregnating ability, tow spreading ability, and covering ability at the time of forming a cloth.
The carbon fiber precursor fiber bundle according to a first embodiment of the present invention is characterized in comprising a plurality of monofilaments of acrylonitrile-based polymer, wherein the ratio of the length and width of the fiber cross section of the monofilament (length/width) is 1.05 to 1.6, and the amount of Si measured by ICP atomic emission spectrometry is in the range of 500 to 4,000 ppm.
The aforementioned carbon fiber precursor fiber bundle has a high compactness and excellent carbonizing processing ability. In addition, the carbon fiber bundle obtained therefrom possesses an excellent resin impregnating ability and tow spreading ability, in addition to a high strength and high bulkiness.
In addition, the monofilament strength within this carbon fiber precursor fiber bundle is preferably at least 5.0 cN/dtex. As a result, the generation of fluff secondary to cutting of the monofilaments during the baking process is reduced, which in turn leads to further improvement of the carbonizing processing ability.
In addition, the center line average height (Ra) of the monofilament surface of the carbon fiber precursor fiber bundle is preferably 0.01 to 0.1 xcexcm. In this manner, it is possible to further improve the compactness and carbonizing processing ability of the carbon fiber precursor fiber bundle, and also further improve the resin impregnating ability, tow spreading ability, and strength of the carbon fiber bundle obtained therefrom.
In addition, the maximum height (Ry) of the monofilament surface of the carbon fiber precursor fiber bundle is preferably 0.1 to 0.5 xcexcm. In this manner, it is possible to further improve the compactness and carbonizing processing ability of the carbon fiber precursor fiber bundle, and also further improve the resin impregnating ability, tow spreading ability, and strength of the carbon fiber bundle obtained therefrom.
In addition, this carbon fiber precursor fiber bundle is further characterized in comprising a plurality of wrinkles extending in the longitudinal direction on the surface of the monofilament, wherein the interval (S) between neighboring local peaks is within the range of 0.2 to 1.0 xcexcm. In this manner, it is possible to further improve the compactness and carbonizing processing ability of the carbon fiber precursor fiber bundle, and also further improve the resin impregnating ability, tow spreading ability, and strength of the carbon fiber bundle obtained therefrom.
In addition, the water content of this carbon fiber precursor fiber bundle is preferably no greater than 15 wt. %. In this manner, the monofilaments of the fiber bundle are easily confounded, thereby further improving the carbonizing processing ability.
In addition, the number of monofilaments comprising this carbon fiber precursor fiber bundle is preferably no greater than 12000. In this manner, it is possible to increase the spinning rate of the carbon fiber precursor fiber bundle. In addition, it is also possible to impart uniform confounding, and as a result, improve the processing ability during the baking process.
In addition, the confounding degree of the carbon fiber precursor fiber bundle is preferably within the range of 5/m to 20/m. In this manner, the carbonizing processing ability of the carbon fiber precursor fiber bundle is further improved, which in turn leads to further improvement of the resin impregnating ability and tow spreading ability of the carbon fiber bundle obtained therefrom.
The carbon fiber precursor fiber bundle according to a second embodiment of the present invention is characterized in comprising a plurality of monofilaments of acrylonitrile-based polymer, wherein the liquid content ratio HW, calculated according to the following method, is at least 40 wt. % and no greater than 60 wt. %.
(Liquid Content Ratio Calculation Method)
The liquid content ratio HW is calculated using the following equation from the absolute dry weight W0 of the fiber bundle following removal of an oiling agent and drying to a absolute dry state, and the fiber bundle weight WT after soaking this fiber bundle in distilled water at 20xc2x0 C. under zero tension for one hour and then performing compression dehydration under a pressure of 200 kPa.
HW(wt. %)=(WTxe2x88x92W0)/W0xc3x97100 
The carbon fiber bundle obtained from this carbon fiber precursor fiber bundle has an improved bulkiness, and a superior resin impregnating ability, tow spreading ability, and covering ability at the time of forming a cloth.
In addition, the center line average height (Ra) of the monofilament surface of this carbon fiber precursor fiber bundle is preferably at least 0.01 xcexcm. In this manner, the bulkiness of the carbon fiber bundle is further improved, which in turn leads to further improvement of the resin impregnating ability, tow spreading ability, and covering ability at the time of forming a cloth.
In addition, the maximum height (Ry) of the monofilament surface of this carbon fiber precursor fiber bundle is preferably at least 0.1 xcexcm. In this manner, the bulkiness of the carbon fiber bundle is further improved, which in turn leads to further improvement of the resin impregnating ability, tow spreading ability, and covering ability at the time of forming a cloth.
In addition, this carbon fiber precursor fiber bundle is further characterized in comprising a plurality of wrinkles extending in the longitudinal direction on the surface of the monofilament, wherein the interval (S) between neighboring local peaks is preferably at least 0.2 xcexcm, and no greater than 1.0 xcexcm. In this manner, it is possible to maintain the excellent carbonizing processing ability of the carbon fiber precursor fiber bundle, and further improve the resin impregnating ability, tow spreading ability of the carbon fiber bundle obtained therefrom, and covering ability at the time of forming a cloth.
In addition, the water content of this carbon fiber precursor fiber bundle is preferably no greater than 15 wt. %. In this manner, the monofilaments of the carbon fiber precursor fiber bundle are easily confounded, thereby further improving the carbonizing processing ability thereof.
In addition, the number of monofilaments comprising this carbon fiber precursor fiber bundle is preferably no greater than 12000. In this manner, it is possible to increase the spinning rate of the carbon fiber precursor fiber bundle. In addition, it is also possible to impart uniform confounding, and as a result, improve the processing ability during the baking process.
In addition, the confounding degree of the carbon fiber precursor fiber bundle is preferably within the range of 5/m to 20/m. In this manner, it is possible to maintain the excellent carbonizing processing ability of the carbon fiber precursor fiber bundle, and further improve the resin impregnating ability and tow spreading ability of the carbon fiber bundle obtained therefrom, and covering ability at the time of forming a cloth.
The carbon fiber precursor fiber bundle according to a third embodiment of the present invention is characterized in comprising a plurality of monofilaments of acrylonitrile-based polymer, wherein the ratio of the length and width of the fiber cross section of the monofilament (length/width) is 1.05 to 1.6; the amount of Si measured by ICP atomic emission spectrometry is in the range of 500 to 4,000 ppm; and the liquid content ratio HW, calculated according to the aforementioned method, is at least 40 wt. % and less than 60 wt. %.
The carbon fiber precursor fiber bundle formed according to the aforementioned displays a high compactness and excellent carbonizing processing ability, and is able to provide a carbon fiber bundle possessing an excellent resin impregnating ability and tow spreading ability, in addition to a high strength and high bulkiness. In addition, the carbon fiber bundle obtained from the aforementioned carbon fiber precursor fiber bundle possesses an improved bulkiness, in addition to a superior resin impregnating ability, tow spreading ability, and covering ability at the time of forming a cloth.
In addition, the method for manufacturing a carbon fiber precursor fiber bundle according to the present invention comprises the steps of:
extruding a spinning solution which is a solution of an organic solvent and an acrylonitrile-based polymer containing at least 95 wt. % of the acrylonitrile unit into a first coagulation bath formed from an aqueous solution of an organic solvent comprising the organic solvent concentration of 45 to 68 wt. % and a temperature of 30 to 50xc2x0 C. to form solid fibers;
taking-up solid fibers at a take-up speed no greater than 0.8 times an extrusion linear speed of the spinning solution from the first coagulation bath;
drawing solid fibers by 1.1xcx9c3.0 fold in a second coagulation bath formed from an aqueous solution of an organic solvent comprising the organic solvent concentration of 45 to 68 wt. % and a temperature of 30 to 50xc2x0 C. to form drawn fibers; and
steam-drawing drawn fibers by 2.0xcx9c5.0 fold after drying drawn fibers.
According to this method for manufacturing a carbon fiber precursor fiber bundle, a carbon fiber precursor fiber bundle possessing the aforementioned superior properties may be easily manufactured.